Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 221130
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
530 AM CST SAT NOV 22 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 415 AM CST SAT NOV 22 2014

FOG AND STRATUS SHOULD PERSIST FROM NW IA INTO PART OF SW MN
INTO THE LATE MORNING WHEN LOW LEVEL SWRLY FLOW AND SOME
WARMING WILL BE SWEEPING IT OUT. FOG WILL CONTINUE TO GET
MARGINALLY DENSE IN SOME AREAS BUT WIDESPREAD DENSE FOG HAD NOT
DEVELOPED...AND WITH A CONTINUING DECENT LOW LEVEL FLOW IN THAT AREA
SUSPECT WE WILL NOT NEED A DENSE FOG ADVISORY...BUT OF COURSE WILL
MONITOR NEXT FEW HOURS. SOME VERY PATCHY SHALLOW FOG WILL
CONTINUE TO DEVELOP FURTHER WEST BUT DRIER AIR NOT MUCH ABOVE THE
SURFACE SHOULD PREVENT MUCH. ASIDE FROM SOME STRATUS LINGERING
FAR EAST INTO PERHAPS THE EARLY AFTERNOON...THE FORECAST AREA IS
EXPECTED TO BE MOSTLY SUNNY TODAY. TEMPERATURES OF COURSE WILL BE
MILD WITH A DECENT ROUND OF SNOWMELT. UPPER 30S NORTHEAST TO THE
LOWER 50S SOUTHWEST LOOKS GOOD FOR HIGHS.

TONIGHT WE EXPECT THAT THE STRATUS WILL REDEVELOP SOUTHEAST AS
HIGHER CLOUDS BEGIN TO INCREASE FROM THE WEST WITH APPROACHING
SYSTEM. THERE SEEMS TO BE ENOUGH MID LEVEL LIFT FOR A FEW LIGHT
SHOWERS TO SPREAD IN FROM THE WEST BUT MODELS ARE SHOWING FAIRLY DRY
AND WILL CONTINUE TO PLAY THE AIR BEING DRY ENOUGH TO PRECLUDE
PRECIPITATION THIS WAY THROUGH THE NIGHTTIME HOURS. THE INCREASE IN
LOW CLOUDS AND THEIR DEPTH OVER NORTHWEST IOWA SUGGESTS SOME DRIZZLE
POSSIBLE LATE TONIGHT...BUT THAT INCREASED DEPTH ALSO SUGGESTS
DROPLETS COULD BE BIG ENOUGH FOR MINIMALLY MEASURABLE LIGHT
RAIN...AND SINCE WE HAVE BEEN CARRYING LOW POPS...WILL CONTINUE
THEM FOR LATE TONIGHT...EVEN THOUGH MID LEVEL SUPPORT FOR RAIN
SEEMS FURTHER SOUTHEAST. TEMPERATURES WILL BE MILD WITH AREAS IN
SOUTHEAST SD NORTH OF INTERSTATE 90 MAYBE COOLING A DEGREE OR TWO
BELOW FREEZING. UNSURE OF THE DEGREE OF LATE NIGHT MIXING WITH
APPROACHING SYSTEM SO WILL NOT GET CUTE WITH ANY SUDDEN TEMPERATURE
JUMPS...BUT THEY COULD HAPPEN.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 415 AM CST SAT NOV 22 2014

DOMINANT FOCUS OF THE START OF THE LONGER TERM IS EVOLUTION OF THE
STRONG SYSTEM TO THE EAST HEADING INTO SUNDAY NIGHT AND MONDAY. AS
THE NORTHERN STREAM ENERGY COMPONENT APPROACHES ON SUNDAY...AT
LEAST A MINIMAL THREAT FOR SOME EARLY DAY PRECIPITATION AS VARIOUS
DEGREE OF SHARPNESS TO TROUGH BEGINS TO SLIDE ACROSS THE DAKOTAS.
IF NOT FOR A FEW MODELS/RUNS INDICATING THE MID LEVEL FRONTAL ZONE
ACTUALLY UNDERGOING WEAKENING HEADING ACROSS THE CWA DURING THE
MORNING...WOULD JUSTIFY PERHAPS STRONGER ON THE POPS FOR THE MORNING
AND EARLY AFTERNOON. THERE IS A BIT OF CONCERN ON PRECIPITATION
TYPE POTENTIAL WITH FAIRLY WARM TEMPS ALOFT BATTLING WHAT IS
CERTAIN TO BE A FAIRLY DECENT WET BULB IMPACT. PROBABLY A MIX OF
RAIN OR SNOW...OR EVEN ALL LIGHT SNOW IF CAN GET A BIT MORE
INTENSE OR BANDED PER NAM TYPE SOLUTION. FURTHER SOUTHEAST...
AHEAD OF THE LOW LEVEL WIND SHIFT...WILL LIKELY FIND A MURKY MESS
OF LOWER CLOUDS...SOME FOG...AND CHANCE OF DRIZZLE/LIGHT RAIN IN
THE EARLY MORNING. THIS WILL GET QUICKLY SHOVED ASIDE BY SHIFT IN
WINDS TO THE NORTHWEST. INITIALLY NOT A VERY STRONG COLD PUSH...
WHICH SHOULD ALLOW TEMPS TO RETURN TO THE LOWER 40S ACROSS THE
SOUTHEAST HALF. HOWEVER...COLDER AIR WILL REALLY START TO SURGE
INTO THE AREA DURING THE AFTERNOON...WITH A 6-8C DROP IN 925 HPA
TEMPS LIMITING MIXING BY MIDDAY NORTHWEST...MID AFTERNOON CENTRAL...
AND LATE DAY SOUTHEAST CWA...AND MOST CERTAINLY ENDING WITH A MORE
THAN TYPICAL LATE DAY DROP. WINDS WILL ALSO INCREASE TO 20 TO 30
MPH BY LATE DAY OVER MUCH OF SE SD.

OVERNIGHT IS WHEN THE MERGING OF THE SOUTHERN STREAM AND NORTHERN
STREAM ENERGY OCCURS...BUT WILL BE TO THE EAST...AND IMPACT WILL
BE MAINLY TO THE WIND FIELDS ACROSS THE AREA. GFS IS FAR STRONGER
WITH CYCLOGENESIS...SOMEWHAT FURTHER EASTWARD. WHATEVER SOLUTION
IS MORE CORRECT IN THE END...OUR AREA IS SURE TO EXPERIENCE VERY
STRONG AND GUSTY WINDS FROM 25 TO 45 MPH...AND A TENDENCY FOR THE
SUNDAY NIGHT INTO MONDAY PERIOD FOR SOME LIGHTER SNOWFALL TO CYCLE
SOUTHEASTWARD ACROSS THE AREA...ESPECIALLY SW MN. APPEARS THAT
TOTALS WILL CERTAINLY BE LIGHT AS DEEPER FORCING CONTINUES TO THE
EAST...BUT COULD SEE SOME HALF INCH OR BIT MORE AMOUNTS ACROSS
SOUTHWEST MINNESOTA BY THE TIME IT ENDS ON MONDAY EVENING.
DESPITE THE WINDS...DO NOT EXPECT ENOUGH NEW SNOWFALL TO CREATE
ANY BLOWING SNOW ISSUES...AND THE OLDER SNOW WILL BE WELL CRUSTED
FROM WARMING ABOVE FREEZING FOR A COUPLE DAYS.

FOR THE CRITICAL THANKSGIVING TRAVEL TIME...BY TUESDAY AND
WEDNESDAY...THE AGREEMENT IN THE LONGER WAVE PATTERN IS THERE IN
A GENERAL SENSE...BUT THE IMPORTANT DETAILS ARE VASTLY DIFFERENT.
MOST SOLUTIONS INDICATE A FAIRLY DISTINCT CLIPPER SYSTEM MOVING
FROM NORTH DAKOTA TOWARD CENTRAL MINNESOTA...BUT GFS IS ABOUT 6-9
HOURS QUICKER THAN EC/CANADIAN. TUESDAY WILL PUT CWA INTO A WARMER
SECTOR OF WAVE...AND WILL LIKELY SEE TEMPS PUSH INTO THE 35 TO 40
DEGREE RANGE OVER THE SOUTHWEST HALF OF THE AREA. HAVE PUSHED UP
TIMING FOR A BURST OF SNOWFALL WITHIN THE WARM AIR ADVECTION ZONE
TUESDAY NIGHT... BUT WITH THE STRONGER AND DEEPER FORCING
REMAINING JUST NORTHEAST OF THE AREA...HAVE KEPT THINGS AS A
CHANCE POP FOR THE TIME. THIS IS WHERE THINGS START TO DIVERGE
SIGNIFICANTLY...WITH EC SO AMPLIFIED WITH THIS CLIPPER WAVE THAT
THE THERMAL BOUNDARY IS DRIVEN SO FAR SOUTHWARD THAT ARCTIC RIDGE
TAKES OVER AND IS SIMPLY COLD AND DRY THROUGH THE END OF THE WEEK.
THE GFS/CANADIAN ARE NOT AS AMPLIFIED...GFS LEAST SO...AND THEN
FIND APPROACH OF THE NEXT SUBTLE NORTHERN STREAM WAVE IN A
FAVORABLE LOCATION TO INTERACT WITH THERMAL RIBBON...RESULTING IN
A BAND OF LIGHT PRECIPITATION ACROSS THE AREA...EITHER MAINLY
NORTH PER 00Z GFS...OR THROUGH THE HEART PER 06Z GFS...OR THE
MISSOURI VALLEY PER CANADIAN. QPF/SNOW RATIOS OF 18-20/1 WOULD
BRING PERHAPS 1 TO 3 INCHES OF SNOWFALL IN A WORST CASE AT THIS
POINT. COULD NOT GET A REGIONAL CONSENSUS ON INTRODUCING POPS WITH
INITIALIZATION GRIDS SUB MEASURABLE FOR MOST ON WEDNESDAY INTO
WEDNESDAY EVENING...SO HAVE DEFERRED TO LATER FORECASTS IN HOPES
GUIDANCE CONVERGES ENOUGH TO SUPPORT MORE REASONABLE POPS. ARCTIC
HIGH SETTLES SOUTHWARD THROUGH THANKSGIVING TO GIVE TEMPS WELL
BELOW NORMAL ONCE AGAIN...WITH A LITTLE RECOVERY EXPECTED FRIDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 526 AM CST SAT NOV 22 2014

CEILINGS BELOW 1K FEET AND VISIBILITY BELOW 3SM IN FOG ALONG AND
EAST OF A SUX/FSD/MML LINE...IMPROVING TO VFR BY 17Z. WEST OF A
SUX/FSD/MMML LINE VFR. VFR CONDITIONS SHOULD CONTINUE THROUGH
23/06Z. FROM 23/06Z-12Z CEILINGS BELOW 1K FEET AND VISIBILITIES
BELOW 3SM IN FOG ARE LIKELY TO REDEVELOP OVER NORTHWEST IA
INCLUDING SUX TAF SITE.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR MNZ080-081-
     089-090-098.

IA...DENSE FOG ADVISORY UNTIL 9 AM CST THIS MORNING FOR IAZ001>003-
     012>014-021-022-032.

NE...NONE.
&&

$$

SHORT TERM...
LONG TERM...CHAPMAN
AVIATION...



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